CN103485773A - Method for determining multi-branch horizontal well branch parameters - Google Patents

Abstract

The invention discloses a method for determining multi-branch horizontal well branch parameters. The method mainly comprises the following steps of 1 determining main branch directions, 2 determining branch angles, 3 determining branch numbers and 4 determining branch lengths, wherein the method for determining main branch directions in the step 1 is that when the original permeability of a coal reservoir is good, hole fractures develop and have good directivity, at the moment, the main branch directions should be parallel with or nearly parallel with the directions of main fractures, and the main fractures are connected in series through branches. According to the method, different branch parameters can be determined according to difference of reservoir geologies, the technical method effectively avoids the problems that the design subjectivity is strong due to man-made experienced intervention and numerical simulation software can not be accurately designed effectively according to geology and reservoir conditions, gas extraction blind areas or overlapped areas of branch wells are effectively avoided, development risks are lowered, and extraction efficiency is greatly improved.

Description

A kind of definite method of multi-branched horizontal well branch parameter

Technical field

What the present invention relates to is a kind of coal gas layer production practice technical method, is specifically related to a kind of definite method of multi-branched horizontal well branch parameter.

Background technology

Along with the raising of expanding economy and living standards of the people, more and more higher to the requirement of demand for energy and environmental quality.Cause the processing of coal mine gas to be changed to efficient utilization by directly emptying, the threat that not only can reduce the directly emptying environment pollution caused and bring to the colliery safety in production, and can be used as a kind of new resources, make up to a certain extent the deficiency of conventional resource.The exploitation of gas is mainly to take underground gas extraction and ground extraction as main, and wherein the ground gas extraction is high with its extraction concentration, the extraction time is long, extinction is effective and be developed rapidly.

The ground gas extraction comprises straight well extraction and horizontal well extraction, and wherein the horizontal well extraction is rapidly developed greatly with high, the effective control range of its gas production.While carrying out the multi-branched horizontal well construction, reasonably branch design not only can effectively reduce the construction works amount, and can carry out effective extraction to the gas in control range, reduce overlay region and the blind area of gas pumping, the purpose of reach cost-saving, increasing economic efficiency.But at the scene in the practice of construction process, current branch parameter design major part is based on field experience or numerical simulation software, numerical simulation software is mostly from abroad, the otherness of external geological conditions and Chinese Geological condition causes the attribute of coal seam reservoirs own to exist larger difference to determine that there are larger difference in employing numerical simulation software analog result and actual result, cause human intervention excessive according to field experience.The Multilateral Wells construction investment is large, risk is higher, if parameter designing is unreasonable, easily cause branch not carry out effective extraction to the gas in limit of mining, there are pumping blind zone or overlay region, if exist overlay region virtually to cause the construction waste, if exist pumping blind zone gas effectively not reduce, the gas actual conditions are held and forbidden, may further strengthen the possibility of Gas Outburst.Therefore in the urgent need to a kind of process, can be according to the reservoir actual conditions, the parameters such as the angle of main Zhi Changdu, main and branch, branch length are optimized and determine, so that more effective minimizing pumping blind zone and overlay region, reduce development cost, increase economic efficiency to greatest extent.

Summary of the invention

The present invention seeks to for the main methods such as field experience or numerical simulation that rely on of branch parameter design in the multi-branched horizontal well work progress, easily cause blind area or the overlay region problem of extraction, the definite process of a kind of multi-branched horizontal well branch parameter has been proposed, by this technique, can to the major parameter of multilateral well, be determined according to situations such as zones of different reservoir characteristic, structures, reduce development risk, improved to greatest extent economic benefit.

Definite method of this multi-branched horizontal well branch parameter mainly comprises following four steps: 1. determining of main Zhi Fangwei, 2. determining of branch's angle, 3. determining of number of branches and determining of 4. branch length; Wherein, in described step 1, definite method of main Zhi Fangwei is for when the coal seam reservoirs primary permeability is relatively good, and the porous dehiscence gap is grown, and has directionality preferably, now main Zhi Fangxiang should be parallel or approximate with main fissure direction parallel, by branch, main crack is together in series.

In described step 2, definite method of branch's angle is to establish in coal seam face cleat and the end hugger that is uniform-distribution with crack length and width homogeneous, then ignore each wriggling movement in coal seam while creeping into, and establish to creep into all the time and carry out in same plane, and each branch remains consistent with the angle of main while creeping into; Face cleat and main Zhi Pinghang, coal seam is horizontal seam, and the distance when creeping between each branch equates, then can by the starting pressure gradient ask for row while adopting each branch affect distance, the calculating publicity of the permeability of its starting pressure gradient and coal seam reservoirs is as follows:

λ＝ak ^-b

In formula: λ is the starting pressure gradient, MPa/m; A, b is constant, can be asked for by the experimental data matching; K is the coal seam reservoirs permeability, mD.

If the minimum value of i son field internal pressure decline is p _i, coal seam reservoirs pressure is P, the impact of i son field is apart from S _ican be expressed as:

$S_i=\frac{P-P_i}{a_i{k_i}^{-b_i}}$

At the homonymy of main, with the minimum value of i branch adjacent i+2 son field internal pressure decline be P _i+2, the impact of i+2 son field is apart from S _i+2can be expressed as:

$S_{i+2}=\frac{P-P_{i+2}}{a_{i+2}{k_{i+2}}^{-b_{i+2}}}$

When the coal seam reservoirs original permeability is low, when row adopts, two son fields impact distance separately is smaller, and the angle between these two son fields and main propping up is 20-30 °;

When the coal seam reservoirs original permeability is higher, starting pressure gradient when fluid flows is relatively little, the angle that angle when row adopts between these two son fields and main propping up is 50-60 °.

In described step 3, definite method of number of branches is that to make fluid in that of the farthest required minimum pressure that occurs to flow while adopting be P in the row of establishing _j, when row adopts, critical desorption pressures is P _l, distal-most end place branch desorb distance is:

$S_j=\frac{P_l-P_j}{a_j{k_j}^{-b_j}}$

The minimum pressure that fluid flows in the J-2 branch of its homonymy needs is P _j-2, it is P that row adopts critical desorption pressures _l, this branch's desorb distance can be expressed as:

$S_{j-2}=\frac{P_l-P_{j-2}}{a_{j-2}{k_{j-2}}^{-b_{j-2}}}$

If this desorb radius is the optimal distance of two branches, main Zhi Changdu is L, and the fragmented master of that of distal-most end props up end-to-end distance from being L _j, divide number to be expressed as:

$n=\left[\frac{2(L-L_j)}{S_j+S_{j-2}}\right]+1$

When reservoir permeability is relatively good, fluid flow resistance is less, and a less minute number just can be realized large-scale control.

In described step 4, definite way of branch length is, the barometric gradient of establishing on Multilateral Wells end and head end unit length when fluid flows is i, and the air content of coal seam reservoirs is equal everywhere, is V, and Lan Shi pressure is P _l, the Lan Shi volume is V _l, the minimum pressure that the Multilateral Wells head end can reduce is P _smin, Multilateral Wells length is L, minimum pressure when Multilateral Wells end row adopts is

P _mmin=P _smin+iL

If the permeability in coal seam is all equal on all directions, permeability is k, and establishing water mobile starting pressure gradient in coal seam reservoirs is λ, and the pass between starting pressure gradient and permeability is:

λ＝ak ^b

Wherein: a, the b value is fitting coefficient, can be obtained by laboratory tests.

If when fluid flows in coal seam, the resistance gradient equates, when row adopts in branch's control range from branch's head end to end, the coal seam far-end is to the air content distribution obedience linear change rule in branch well cylinder.The thickness in coal seam is equal everywhere, is h, and the density of coal is ρ, and the gas desorption quantity in the branch length control range can be expressed as:

When the gas desorption quantity in the branch length control range reaches maximum value, drilling equipment creep into length still in allowed limits, and creep in the situation that risk do not increase greatly, think the optimum length that this length is Multilateral Wells, can determine the length of Multilateral Wells.

Owing to having adopted above technical scheme, the present invention has following beneficial effect: can be according to the difference of reservoir geology, carry out determining of different branch parameter, this process has effectively been avoided the problem that can not effectively design more accurately according to geology, reservoir situation that the design subjectivity is strong and numerical simulation software designs caused due to artificial experience intervention, blind area or the overlay region of Multilateral Wells mash gas extraction have effectively been avoided, development risk reduces, and extraction efficiency improves greatly.

The specific embodiment

For technological means, character of innovation that the present invention is realized, reach purpose and effect is easy to understand, below will the technical scheme in the embodiment of the present invention be clearly and completely described.

This specific embodiment comprises following four steps: 1. determining of main Zhi Fangwei, 2. determining of branch's angle, 3. determining of number of branches and determining of 4. branch length; Wherein, definite reservoir permeability and reservoir fracture developmental state of being based on of described main Zhi Fangwei; Described branch angle definite is the difference according to reservoir starting pressure gradient, the effective radius of influence of branch determined, thereby further determined rational branch angle; The definite of described number of branches is to determine according to reservoir pressure, critical desorption pressures, and farthest branch pressure also can be dropped to below critical desorption pressures in a big way; Described branch length definite is according to permeability, drilling cost, creeps into risk etc. and consider, and production capacity is maximized.

1. horizontal well master Zhi Fangwei's determines

It is the central core of circulation of linked hole crack and pit shaft that the horizontal well master props up, and reasonably main design has important impact to horizontal productivity.

When the coal seam reservoirs primary permeability is relatively good, the porous dehiscence gap is grown, there is directionality preferably, now main Zhi Fangxiang should be parallel or approximate with main fissure direction parallel, by branch, main crack is together in series, can make like this gas in the porous dehiscence gap enter fast main by branch, greatly reduce the gas flow resistance, accelerate the output of coal bed gas.

When reservoir permeability is poor or the directionality of reservoir permeability when poor, the orientation of main is less on the Coalbed Methane Productivity impact, and the design of main Zhi Fangwei is mainly to avoid the structure development district such as some tomographies.

1. horizontal well branch angle determines

Multi-branched horizontal well branch angle affects the circulation of number of branches, effective control range, aerogenesis passage etc., so reasonably branch's angle is very large on the production capacity impact.Owing to affecting, horizontal well branch angle factor is a lot, mainly is based on horizontal well so following and divides the prerequisite that number is the same, and its branch's angle is optimized.

If be uniform-distribution with face cleat and the end hugger of crack length and width homogeneous in coal seam, then ignore each wriggling movement in coal seam while creeping into, and establish to creep into all the time and carry out in same plane, and each branch remain consistent with main angle of propping up while creeping into; Face cleat and main Zhi Pinghang, coal seam is horizontal seam, and the distance between each branch equates when creeping into.

The production of coal bed gas well is mainly drainage and step-down, by draining, reduces reservoir pressure, makes pressure reach critical desorption pressures and starts the desorb aerogenesis later.Therefore, can water flow, discharge and discharge the ability that how much has determined to a great extent gas desorption.Row while adopting, affect the mobile many factors of fluid, and wherein principal element is that pressure and the row of row's difference while adopting adopts the difference that pressure reduction between the well bottom pressure reaches resistance between the two and determining to a great extent to arrange the scope that while adopting, pit shaft can affect.Simultaneously, when fluid flows, exist starting pressure, starting pressure gradient and frictional resistance jointly to form the mobile resistance of fluid, and the pressure differential between shaft bottom is the mobile power of fluid, the relativeness between power and resistance, determined whether fluid can flow.So can by the starting pressure gradient ask for row while adopting each branch affect distance.Great many of experiments shows, the permeability of starting pressure gradient and coal seam reservoirs meets following relation:

λ=ak ^-b

In formula: λ is the starting pressure gradient, MPa/m; A, b is constant, can be asked for by the experimental data matching; K is the coal seam reservoirs permeability, mD.

If the minimum value of i son field internal pressure decline is p _i, coal seam reservoirs pressure is P, the impact of i son field is apart from S _ican be expressed as:

$S_i=\frac{P-P_i}{a_i{k_i}^{-b_i}}$

At the homonymy of main, with the minimum value of i branch adjacent i+2 son field internal pressure decline be P _i+2, the impact of i+2 son field is apart from S _i+2can be expressed as:

$S_{i+2}=\frac{P-P_{i+2}}{a_{i+2}{k_{i+2}}^{-b_{i+2}}}$

If the coal seam reservoirs original permeability is relatively low, when row adopts, two son fields impact distance separately is smaller, when two son field spacings are relatively large, cause row while adopting the not influence area between two son fields relatively large, in this case, in order to reduce the not influence area between son field as far as possible, consider the operability of financial cost and drilling well simultaneously, angle between suggestion branch and main propping up should be less, the general angle of selecting 30 °, along with reducing of branched angulation, although branch's maximum of control distance has reduced, but whole controls of control area between branch have been realized, effectively avoided the blind area of extraction between branch.

When the coal seam reservoirs primary permeability is relatively good, starting pressure gradient when fluid flows is relatively little, impact distance when row adopts between son field is relatively long, when pressure drop arrives minimum value, almost can cover between two branches, in this case, in order to reduce the expense of drilling well branch length as far as possible, consider the operability of drilling well simultaneously, angle between suggestion branch and main propping up should be more greatly, the general angle of selecting 60 °, because reservoir permeability is relatively good, effective influence basin of branch is larger, so suitably increase branch's angle, can effectively increase the maximum control range of branch, do not increasing under the prerequisite of creeping into engineering quantity, improved the single well-controlled scope.Not only guarantee extracting result preferably, and lowered regional drilling cost.

Maximum pressure drop when in summary, the distance between the angle of Multilateral Wells and coal seam reservoirs original permeability, son field, row adopt etc. are relevant.While considering drilling cost, when the coal seam reservoirs original permeability is relatively better, should select the angle between branch and main propping up relative large; When the coal seam reservoirs original permeability compares when poor, should select the angle between branch and main relative less; Different permeability inferior division angle wherein, along with permeability reduces gradually, branch's angle reduces gradually, when actual design, can select rational branch angle according to the actual permeability situation of study area reservoir, and wherein part branch angle reference value is as shown in table 1.

3. the horizontal well number of branches determines

The number of Multilateral Wells both with Multilateral Wells between spacing relevant, simultaneously also relevant with the coal seam reservoirs energy system.The number of optimum Multilateral Wells should be also can be reduced to below critical desorption pressures in a big way adopting that pressure when row adopts apart from farthest from row, and more gas output is arranged.

If the mobile required minimum pressure of fluid generation of arranging while adopting in that makes farthest is P _j, when row adopts, critical desorption pressures is P _l, distal-most end place branch desorb distance is:

$S_j=\frac{P_l-P_j}{a_j{k_j}^{-b_j}}$

The minimum pressure that fluid flows in the J-2 branch of its homonymy needs is P _j-2, when row adopts, critical desorption pressures is P _l, this branch's desorb distance can be expressed as:

$S_{j-2}=\frac{P_l-P_{j-2}}{a_{j-2}{k_{j-2}}^{-b_{j-2}}}$

If this desorb radius is the optimal distance of two branches, main Zhi Changdu is L, and the fragmented master of that of distal-most end props up end-to-end distance from being L _j, divide number to be expressed as:

$n=\left[\frac{2(L-L_j)}{S_j+S_{j-2}}\right]+1$

When reservoir permeability is relatively good, fluid flow resistance is less, and a less minute number just can be realized large-scale control, and along with permeability reduces gradually, number of branches increases gradually.When permeability is too poor, do not bore necessity of branch.Wherein the part number of branches determines that reference value is as shown in table 1.

4. Multilateral Wells length determines

When relatively grow in the crack in coal seam, the effect length of branch horizontal well the disappointing area of coal seam reservoirs.In practice, cranky advancing when drilling tool creeps in coal seam, row has increased the mobile resistance of fluid while adopting virtually, and Multilateral Wells length is longer, and the mobile resistance of fluid is larger, and the pressure differential of Multilateral Wells end and head end is larger.Can to the maximum length of branch, be estimated in the following method.If barometric gradient when on Multilateral Wells end and head end unit length, fluid flows is i, the air content of coal seam reservoirs is equal everywhere, is V, and Lan Shi pressure is P _l, the Lan Shi volume is V _l, the minimum pressure that the Multilateral Wells head end can reduce is P _smin, Multilateral Wells length is L, minimum pressure when Multilateral Wells end row adopts is

P _mmin=P _smin+iL

The permeability of supposing coal seam is all equal on all directions, and permeability is k, and establishing water mobile starting pressure gradient in coal seam reservoirs is λ, and the pass between starting pressure gradient and permeability is:

λ＝ak ^b

Wherein: a, the b value is fitting coefficient, can be obtained by laboratory tests.

While supposing that fluid flows in coal seam, the resistance gradient equates, when row adopts in branch's control range from branch's head end to end, the coal seam far-end is to the air content distribution obedience linear change rule in branch well cylinder.The thickness in coal seam is equal everywhere, is h, and the density of coal is ρ, and the gas desorption quantity in the branch length control range can be expressed as:

When the gas desorption quantity in the branch length control range reaches maximum value, drilling equipment creep into length still in allowed limits, and creep in the situation that risk do not increase greatly, think the optimum length that this length is Multilateral Wells.Above-mentioned formula is carried out to differentiate, can determine the length of Multilateral Wells.

Permeability is the Dominated Factors that determines branch length, and when permeability is relatively good, fluid flow resistance in branch is less, has less energy loss, reservoir pressure can be reduced to smaller value, should suitably increase branch length, increases effective control range.Along with permeability reduces, branch length reduces gradually, when permeability hour, flow resistance is excessive, is difficult to reservoir pressure is reduced to smaller value, so should design less branch length.

Calculated the branch parameter under the different permeability by above-mentioned definite method.When permeability is relatively good, single Zhi Youxiao control range is large, flow resistance is little, so branch and main Zhi Changdu are long, number of branches is less, branched angulation is larger; Along with permeability reduces gradually, effectively control range reduces, and flow resistance increases, so branch and main Zhi Changdu diminish, number of branches increases, branched angulation diminishes.When permeability is too small, because effectively influence basin is too small, so need not be in the construction of carrying out branch.

This specific embodiment is that coal seam reservoirs has been used as to solving that homogeneous reservoir carries out, in actual life, coal seam reservoirs is heterogeneous, and the difference of seam inclination, coal seam thickness, coal seam reservoirs pressure, coal-bed gas content, head etc. pressure propagation path, propagation distance and then affect the gas production of coal bed gas well all will affect the multiple-limb well array and adopt the time.And the otherness of geological conditions, mechanical property of coal seam, roof and floor mechanical properties of rock, groundwater dynamics condition etc. all will affect and creep into risk, these have all determined to be undertaken than objective appraisal by a more unified standard.At this, in the situation that do not consider tomography, karst collapse col umn impact, drawn the reference value of branch parameter, the reference of optimizing as on-the-spot branch parameter, as shown in table 1.，

The reference value of table 1 different reservoir physical property Coal Under layer gas multilateral well branch parameter

Finally it should be noted that: above embodiment only, in order to technical scheme of the present invention to be described, is not intended to limit; Although with reference to previous embodiment, the present invention is had been described in detail, those of ordinary skill in the art should be appreciated that its technical scheme that still can put down in writing aforementioned each embodiment modifies, or part technical characterictic wherein is equal to replacement; And these modifications or replacement do not make the essence of appropriate technical solution break away from the spirit and scope of various embodiments of the present invention technical scheme.

Claims (4)

1. definite method of a multi-branched horizontal well branch parameter, mainly comprise following four steps: 1. determining of main Zhi Fangwei, 2. determining of branch's angle, 3. determining of number of branches and determining of 4. branch length; Wherein, in described step 1, definite method of main Zhi Fangwei is for when the coal seam reservoirs primary permeability is relatively good, and the porous dehiscence gap is grown, and has directionality preferably, now main Zhi Fangxiang should be parallel or approximate with main fissure direction parallel, by branch, main crack is together in series.

2. definite method of a kind of multi-branched horizontal well branch parameter according to claim 1, it is characterized in that in described step 2, definite method of branch's angle is to establish in coal seam face cleat and the end hugger that is uniform-distribution with crack length and width homogeneous, then ignore each wriggling movement in coal seam while creeping into, and establish to creep into all the time and carry out in same plane, and each branch remains consistent with the angle of main while creeping into; Face cleat and main Zhi Pinghang, coal seam is horizontal seam, and the distance when creeping between each branch equates, then can by the starting pressure gradient ask for row while adopting each branch affect distance, the calculating publicity of the permeability of its starting pressure gradient and coal seam reservoirs is as follows:

λ＝ak ^-b

In formula: λ is the starting pressure gradient, MPa/m; A, b is constant, can be asked for by the experimental data matching; K is the coal seam reservoirs permeability, mD.

If the minimum value of i son field internal pressure decline is p _i, coal seam reservoirs pressure is P, the impact of i son field is apart from S _ican be expressed as:

$S_i=\frac{P-P_i}{a_i{k_i}^{-b_i}}$

At the homonymy of main, with the minimum value of i branch adjacent i+2 son field internal pressure decline be P _i+2, the impact of i+2 son field is apart from S _i+2can be expressed as:

$S_{i+2}=\frac{P-P_{i+2}}{a_{i+2}{k_{i+2}}^{-b_{i+2}}}$

When the coal seam reservoirs original permeability is low, when row adopts, two son fields impact distance separately is smaller, and the angle between these two son fields and main propping up is 20-30 °;

When the coal seam reservoirs original permeability is higher, starting pressure gradient when fluid flows is relatively little, the angle that angle when row adopts between these two son fields and main propping up is 50-60 °.

3. definite method of a kind of multi-branched horizontal well branch parameter according to claim 1, is characterized in that definite method of number of branches in described step 3 is that to make fluid in that of the farthest required minimum pressure that occurs to flow while adopting be P in the row of establishing _j, when row adopts, critical desorption pressures is P _l, distal-most end place branch desorb distance is:

$S_j=\frac{P_l-P_j}{a_j{k_j}^{-b_j}}$

The minimum pressure that fluid flows in the J-2 branch of its homonymy needs is P _j-2, it is P that row adopts critical desorption pressures _l, this branch's desorb distance can be expressed as:

$S_{j-2}=\frac{P_l-P_{j-2}}{a_{j-2}{k_{j-2}}^{-b_{j-2}}}$

If this desorb radius is the optimal distance of two branches, main Zhi Changdu is L, and the fragmented master of that of distal-most end props up end-to-end distance from being L _j, divide number to be expressed as:

$n=\left[\frac{2(L-L_j)}{S_j+S_{j-2}}\right]+1.$

4. definite method of a kind of multi-branched horizontal well branch parameter according to claim 1, it is characterized in that in described step 4, definite way of branch length is, if barometric gradient when on Multilateral Wells end and head end unit length, fluid flows is i, the air content of coal seam reservoirs equates everywhere, be V, Lan Shi pressure is P _l, the Lan Shi volume is V _l, the minimum pressure that the Multilateral Wells head end can reduce is P _smin, Multilateral Wells length is L, minimum pressure when Multilateral Wells end row adopts is

P _mmin=P _smin+iL

If the permeability in coal seam is all equal on all directions, permeability is k, and establishing water mobile starting pressure gradient in coal seam reservoirs is λ, and the pass between starting pressure gradient and permeability is:

λ＝ak ^b

Wherein: a, the b value is fitting coefficient, can be obtained by laboratory tests;

If when fluid flows in coal seam, the resistance gradient equates, when row adopts in branch's control range from branch's head end to end, the coal seam far-end is to the air content distribution obedience linear change rule in branch well cylinder.The thickness in coal seam is equal everywhere, is h, and the density of coal is ρ, and the gas desorption quantity in the branch length control range can be expressed as:

When the gas desorption quantity in the branch length control range reaches maximum value, drilling equipment creep into length still in allowed limits, and creep in the situation that risk do not increase greatly, think the optimum length that this length is Multilateral Wells, can determine the length of Multilateral Wells.